This invention relates to fluid-delivery systems.
Chesler, U.S. Pat. No. 2,444,004 ("Chesler"), describes a writing instrument that includes a rigid body having a cavity, a sac within the cavity, and a ball mounted in a writing tip. The sac includes ink in fluid communication with the writing tip. The cavity further includes a spring that applies pressure to the sac to deliver ink to the writing tip. A rigid bar is positioned between the spring and the sac. According to Chesler (col. 3, lines 20-24):
[T]he pressure exerted by the [spring/rigid bar] is substantially as great when the sac is nearly empty as when it is full, and it is therefore nearly uniform.
Chesler does not explain what he means by "nearly uniform." As will be demonstrated later, the pressure applied by the Chesler spring/rigid bar varies from when the sac is filled to when the sac is empty.